COVID-19 Exposed the Need for Increased Research on the Sense of Smell

by Sanya Desai

For the two years, COVID-19 has been the greatest fear of many when they get sick. Many of the symptoms of acute infection mimic a common cold. However infection can lead to a variety of unusual symptoms, including sensory, neurological, gastrointestinal, cutaneous and ocular. One particularly distinctive symptom of COVID-19 is the loss of smell (anosmia) and taste (dysgustia). Though most people with COVID-19 infection develop a self-limited illness lasting 2-14 days, those who get very ill and are hospitalized may not recover for 6 weeks. Those unfortunate enough to get long-haul Covid may not recover for months or longer.

In a review of 21 cross sectional studies across the world, between 33.9 and 68% of COVID positive patients self-reported anosmia. However, the actual numbers may be much higher. In one group of COVID-19 positive people, only 35% self-reported loss of smell but 98% were shown to exhibit loss of smell after administration of the University of Pennsylvania Smell Identification Test. Prior to the current pandemic, anosmia received very little attention in the popular press or medical literature. However, though it may be difficult to quantify, it has become clear that olfactory dysfunction can have significant health effects.

Lesser-known symptoms of COVID-19 also include other forms of olfactory dysfunction. Parosmia is the distortion of specific odors into being perceived as unpleasant. Often affecting common scents like coffee, chocolate, and mint, parosmia always develops after either a viral infection or a traumatic brain injury. One study published in the Rhinology Journal found that 43.1% of people with COVID-19 self-reported parosmia. Often, parosmia will develop as people with anosmia begin to recover.

Meanwhile, anosmia can also lead to many consequential issues, including appetite changes and both over and under-eating. Since smell is involved in our interaction with the environment, anosmia and parosmia put affected individuals at an increased risk of food poisoning and can limit our ability to perceive dangerous odorous gases or smoke in the air. Additionally, we use smell in our interaction with people including ourselves, babies, and intimate partners. Therefore, anosmia can profoundly impact our relationships with individuals and the world around us. Parosmia that affects the scent of mint can result in an aversion to toothpaste and therefore bad hygiene.

Finally, these disorders have serious implications on emotional and mental health, including possibly causing depression and anxiety. Although smell is arguably the least appreciated of the senses, it is fundamentally involved in memory formation, emotional processing and social behavior. COVID-19’s related effects on smell therefore pose potentially serious risks to the infected, including disruptions in quality of life, physical and psychological health, relationships, and sense of self. Current treatments for the virus do not provide any avenues for recovering lost olfactory capabilities. It is likely that some form of olfactory retraining therapy will be required. This should be an alarm for the medical community, mental health community, and scientists to begin further studying the pathophysiological mechanisms involved in this condition and elucidation of potential treatment options.

Because COVID-19 emerged recently, many important questions still remain unanswered. It is intriguing that some of the symptoms of long Covid appear to diminish with vaccination. With COVID-19 related anosmia, we know what types of cells are affected but not what happens inside the cell to impede function and efficacy. It is known that the virus uses the Angiotensin-converting enzyme 2 (ACE2) receptor to attach to a host cell and that ACE2 is found in cells of the olfactory tissue. However, whether this is the mechanism of the loss of smell remains unknown. Parosmia has been studied very little so far, and even the basic molecular pathways are still unknown. It is postulated that regenerating olfactory neurons are undergoing a trial and error process in reconnections with the brain.

It is unfair for patients suffering from olfactory dysfunction to go at this alone. Many have turned to Facebook groups to vent and share ideas. However, now approaching two years since the first people were known to have COVID-19, it's high time that we as a society invest in the research and studies to get some answers.


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